Variable name with internal double-underscore gets snake case warning, but leading/trailing does not

[huonw]

#![allow(unused_variables)]

fn main() {
    let x__y = 0u;

    let __xy = 0u;
    let xy__ = 0u;
}

doubleunder.rs:4:9: 4:13 warning: variable `x__y` should have a snake case name such as `x_y`, #[warn(non_snake_case)] on by default
doubleunder.rs:4     let x__y = 0u;
                         ^~~~

It seems slightly weird that we are inconsistent.

[lilyball]

Are you proposing that we remove the warning for x__y? Allowing xy__ and __xy seems correct.

[huonw]

I'm not proposing either, just wanting us to be consistent either way. (I personally would prefer making all legal.)

[frewsxcv]

1.1.0 Update: The warning is still given for x__y

Playpen: http://is.gd/mmKJtz

[steveklabnik]

Triage: no change.

o_____o

😉

[Mark-Simulacrum]

I think the leading __ case is intentional, but uncertain about trailing.

[steveklabnik]

Triage: no change

[Mark-Simulacrum]

The test case for this lint has two "don't allow two underscores" cases (https://github.com/rust-lang/rust/blob/master/src/test/ui/lint/lint-non-snake-case-functions.rs). I'm going to say that's probably enough that we don't want to just change behavior here -- in particular, it seems no one really wants this. (If they do, I would encourage them to file a PR or chime in here).